1. Field of the Invention
The present invention relates to lightwave packaging techniques for pairs of optical devices and, more particularly, to an optical packaging arrangement particularly suited for transceiver applications which utilizes plastic piece parts and an automated assembly process to provide cost-effective packaging.
2. Description of the Prior Art
There exist many different arrangements for packaging optical transmitters or receivers. For example, an optical device (e.g., laser, LED, APD or PIN photodiode) may be encased in an optical assembly with appropriate lensing and an optical fiber attached to the assembly. The electronics required for operating the optical device includes, for example, a modulation circuit for a transmitter or a detection circuit for a receiver. These circuits are separately assembled (on a printed wiring board, for example) and connected to the housed optical device by conventional electrical leads. Alternatively, the electronics may be fully enclosed in a separate housing, with only the leads exposed for connection to the optical device. An advantage of using separate housings is that many different electronic circuits may be connected to the same optical device. For example, the electronics for a data link application may operate with various types of logic signals (e.g., ECL or TTL) without the need for modifying the package housing to accommodate the different electronics. Additionally, if either the electrical or optical portion of a transmitter or receiver were to experience a failure, the working portion could be disconnected and re-used with another arrangement. A major disadvantage of separate packaging is the increased overall size of the transmitter or receiver. With two separate packages, or an optical package mounted on a printed wiring board, the system requires a rather large space. Further, such a system is susceptible to electrical noise introduced by the necessarily long lead lengths of the connections between the electronics and the optical device. This electrical noise factor becomes a significant concern at bit rates exceeding approximately 10 Mb/s. Also, long leads may limit the maximum bit rate of both the transmitter and receiver, due to parasitic lead inductance (limits the transmitter) and parasitic capacitance (limits the receiver).
These and other concerns have led to the development of package designs which provide for the electronics and optical device to be housed in the same unit. In particular, there exist a number of such unitary arrangements particularly suited for data link applications which utilize an LED as the transmitting device and a PIN photodiode as the receiving device. Many of these unitary packages are relatively expensive, as a result of using machined metallic components. Further, these subassemblies have been known to experience alignment difficulties. There also exist fabrication problems in mating the various piece parts (i.e., outer housing, optical subassembly and electronics). These unitary packages are also known to generate a significant amount of heat, where thermal management of optical data link transmitters and receivers has been a significant problem. Lastly, in many instances, the prior art packaging schemes are limited to either transmitter or receiver applications. Therefore, to utilize a pair of optical devices together at one site (as in a transceiver, for example) a pair of separate packages must be utilized. Again, the use of a pair of packages necessarily increases the cost, size and complexity of the system.
Thus, a need remains in the prior art for improved lightwave packaging arrangements, especially arrangements capable of housing more than one optical device.